Foreign Animal Disease Investigations

"Veterinary practitioners are the cornerstone of foreign animal disease (FAD) surveillance in the United States," said Eileen Ostlund, DVM, PhD, head of the equine and ovine viruses section at the Diagnostic Virology Laboratory, National Veterinary Services Laboratories, in Ames, Iowa, while she was speaking at the Western Veterinary Conference. "Reporting suspicious lesions or unusual clinical signs is the first step in any investigation.

"When I was in practice, I had no idea this system existed," she commented during the Feb. 15-19 convention in Las Vegas, Nev. "But there are more than 200 FAD investigations (FADI) per year--I get notifications almost every day. The USDA Veterinary Services has rapid response capabilities for FADI through specially trained FAD diagnosticians and the federal diagnostic laboratories. Accurate surveillance for foreign and emerging animal diseases is critical in monitoring the health status of U.S. horses, and in facilitating international movement of horses."

Ostlund developed the Western States presentation with Brian McCluskey, DVM, PhD, Dipl. ACVPM, dairy specialist and analytical epidemiologist with the Centers for Epidemiology and Animal Health, Veterinary Services, Animal and Plant Health Inspection Service, USDA. They described FAD and endemic/domestic diseases, and explained the role of private veterinarians and USDA Veterinary Services in a FADI.

The Diseases

"The United States reports animal disease status to the Office International des Epizooties (OIE), the international organization for animal health," Ostlund said. The OIE maintains two lists of significant animal diseases--List A and List B. She described the two lists as follows:

"List A contains the transmissible diseases that have potential for very serious and rapid spread, irrespective of national borders. These have particularly serious socioeconomic or public health consequences and are of major importance in international trade of animals. List A equine diseases include vesicular stomatitis and African horse sickness. List B contains the transmissible diseases that are of socioeconomic and/or public health importance within countries and that are also significant in the international trade of animals and animal products."

She presented the equine diseases listed with the OIE, including notes on their status in the U.S., as follows:

DISEASE
OIE* LIST
COMMENTS
Vesicular Stomatitis
A**
Has occurred in United States; suspect cases must be investigated as a Foreign Animal Disease
African Horse Sickness
A
Not known to occur/foreign/exotic in the United States
Contagious equine metritis (CEM)
B***
Foreign (positive cases have been identified through testing of imported horses)
Dourine
B
Exotic, routine test for imported horses
Epizootic lymphangitis
B
Exotic
Eastern equine encephalomyelitis (EEE)
B
Endemic in Eastern United States, yearly outbreaks occur
Western equine encephalomyelitis (WEE)
B
Endemic in Western United States, no recent U.S. outbreaks
Venezuelan equine encephalomyelitis (VEE)
B
Exotic (horses imported from endemic countries subjected to seven-day quarantine for observation)
Equine infectious anemia (EIA)
B
Endemic in United States, but positive horses prohibited from import into the country, routine test for imported horses
Equine Piroplasmosis
B
Exotic, routine test for imported horses
Equine Rhinopneumonitis
B
Endemic in United States, equine herpesvirus-1 (EHV-1)
Equine Viral Arteritis (EVA)
B
Present in United States, disease problems have occurred after import of virus-shedding stallions
Glanders
B
Exotic, routine test for imported horses
Horse Pox
B
Exotic
Japanese encephalitis
B
Exotic (closely related to West Nile virus)
* Office International des Epizooties, www.oie.int
** OIE LIST A DISEASES: Transmissible diseases that have the potential for very serious and rapid spread, irrespective of national borders, that are of serious socio-economic or public health consequence and that are of major importance in the international trade of animals and animal products. Reports are submitted to the OIE as often as necessary to comply with Articles 1.1.3.2 and 1.1.3.3 of the International Animal Health Code.
*** OIE LIST B DISEASES: Transmissible diseases that are considered to be of socio-economic and/or public health importance within countries and that are significant in the international trade of animals and animal products.
Reports are normally submitted once a year, although more frequent reporting may in some cases be necessary to comply with Articles 1.1.3.2 and 1.1.3.3 of the International Animal Health Code.

Ostlund noted that there is no overlap between diseases considered to be FADs in a particular country and diseases considered endemic or domestic. Emerging diseases, however, can encompass both--such as West Nile virus, which she described as an emerging endemic disease in the United States. Other emerging diseases, she said, include bovine spongiform encephalopathy, mare reproductive loss syndrome, Hendra/Nipah virus, and highly pathogenic avian influenza.

The Practitioner's Role

"The individual client's horse (or horses) is of primary concern to practitioners," Ostlund stated. "But effective treatment depends on accurate diagnosis. The federal government relies on practitioners to bring cases of concern to the attention of appropriate authorities. In turn, through FAD investigations, USDA/APHIS/VS provides diagnostic assistance to the practitioner at no cost.
"What warrants concern?" she asked the audience. She listed the following factors that might tip off a practitioner to a FAD:

  • Unusual clinical presentation;
  • A clinical presentation that is unusual for that area;
  • An unusual age of the affected animal;
  • Higher than usual mortality;
  • Unexpected laboratory results; and/or
  • Higher frequency of a typical clinical presentation.

"So whom do you call?" Ostlund asked. "The Area Veterinarian in Charge (AVIC), the Federal veterinarian assigned to the state/region where the animals are located, should be the first point of contact. The AVIC will assign one or more Foreign Animal Disease Diagnosticians (FADD) to assist with the investigation. FADDs are veterinarians who have received special training in investigating and diagnosing FADs." She said FAD diagnosticians are located "within a couple of hours of almost anywhere," and warned that the clinical signs of many FADs can mimic endemic diseases.

The Investigation
Ostlund described the process of a FADI in the United States as follows:

  1. The owner identifies a problem with a horse or horses and calls a veterinarian.
  2. The practitioner makes a farm call, giving a tentative diagnosis and suspicion of a FAD.
  3. The practitioner calls an animal health official, such as the local FADD, state veterinarian, and/or the AVIC.
  4. The AVIC assigns the investigation to a FADD.
  5. The FADD contacts the owner and practitioner for the animal's history and tentative diagnosis, and schedules a visit.
  6. The FADD does an on-farm investigation, which consists of:
    • Examination of affected and non-affected animals;
    • Collection of appropriate biological samples;
    • History and epidemiological data;
    • Issuing a hold order or quarantine if necessary (Ostlund noted that these are judiciously and rarely employed); and
    • Potential investigation of neighboring premises and tracebacks/traceforwards. (Tracebacks--history of animal movement and contacts prior to illness. Traceforwards--tracing any possible spread of the disease from the index case.)
  7. Samples are submitted to the NVSL. If they are marked Priority 1, they are hand-carried to the lab and processed immediately, Ostlund explained. Priority 2 samples are sent next-day air and processed the same day. Priority 3 samples are sent next-day air and processed according to accession order. There is no charge to the owner or practitioner for these tests, she said.
  8. The results are reported to the AVIC, FADD, owner, and practitioner. If the tests come back negative for FAD, no further action is taken. If any test for a FAD is positive, then the Animal Emergency Response Organization (AERO) is activated.

"It is possible that animal movement may be restricted from the affected premises while the investigation is ongoing," Ostlund said. "When a diagnosis is obtained, the AVIC along with State officials determine further actions."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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